From 8d8cc9087fd44c097775ca0a9ebb6c877605baec Mon Sep 17 00:00:00 2001
From: Vincent Fazio <5265893+vfazio@users.noreply.github.com>
Date: Wed, 28 Feb 2024 13:55:04 -0600
Subject: [PATCH] gh-115382: Fix cross compiles when host and target use same
 SOABI

Previously, when a build was configured to use a host interpreter via
--with-build-python, the PYTHON_FOR_BUILD config value included a path
in PYTHONPATH that pointed to the target's built external modules.

For "normal" foreign architecture cross compiles, when loading compiled
external libraries, the target libraries were processed first due to
their precedence in sys.path. These libraries were then ruled out due to
a mismatch in the SOABI so the import mechanism continued searching
until it found the host's native modules.

However, if the host interpreter and the target python were on the same
version + SOABI combination, the host interpreter would attempt to load
the target's external modules due to their precedence in sys.path.

Despite the "match", the target build may have been linked against a
different libc or may include unsupported instructions so loading or
executing the target's external modules can lead to crashes.

Now, the path to the target's external modules is no longer defined in
PYTHONPATH to prevent accidentally loading these foreign modules.

One caveat is that during certain build stages, the target's sysconfig
module requires higher precedence than the host's version in order to
accurately query the target build's configuration.

This worked previously due to the target's sysconfig data module having
precedence over the host's (see above). In order to keep this desired
behavior, a new environment variable, _PYTHON_SYSCONFIGDATA_PATH, has
been defined so sysconfig can search this directory for the target's
sysconfig data.

Signed-off-by: Vincent Fazio <vfazio@gmail.com>
Upstream-issue: https://github.com/python/cpython/issues/115382
Upstream: https://github.com/python/cpython/pull/116294
---
 Lib/sysconfig.py             | 15 ++++++++++++++-
 Lib/test/libregrtest/main.py |  1 +
 Lib/test/pythoninfo.py       |  1 +
 Tools/scripts/run_tests.py   |  1 +
 configure                    |  2 +-
 configure.ac                 |  2 +-
 6 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/Lib/sysconfig.py b/Lib/sysconfig.py
index 6328ec41af..744f715fe2 100644
--- a/Lib/sysconfig.py
+++ b/Lib/sysconfig.py
@@ -535,7 +535,20 @@ def _init_posix(vars):
     """Initialize the module as appropriate for POSIX systems."""
     # _sysconfigdata is generated at build time, see _generate_posix_vars()
     name = _get_sysconfigdata_name()
-    _temp = __import__(name, globals(), locals(), ['build_time_vars'], 0)
+
+    # For cross builds, the path to the target's sysconfigdata must be specified
+    # so it can be imported. It cannot be in PYTHONPATH, as foreign modules in
+    # sys.path can cause crashes when loaded by the host interpreter.
+    # Rely on truthiness as a valueless env variable is still an empty string.
+    # See OS X note in _generate_posix_vars re _sysconfigdata.
+    if (path := os.environ.get('_PYTHON_SYSCONFIGDATA_PATH')):
+        from importlib.machinery import FileFinder, SourceFileLoader, SOURCE_SUFFIXES
+        from importlib.util import module_from_spec
+        spec = FileFinder(path, (SourceFileLoader, SOURCE_SUFFIXES)).find_spec(name)
+        _temp = module_from_spec(spec)
+        spec.loader.exec_module(_temp)
+    else:
+        _temp = __import__(name, globals(), locals(), ['build_time_vars'], 0)
     build_time_vars = _temp.build_time_vars
     vars.update(build_time_vars)
 
diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index a9725fa967..121e2e7393 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -519,6 +519,7 @@ def _add_cross_compile_opts(self, regrtest_opts):
                 '_PYTHON_PROJECT_BASE',
                 '_PYTHON_HOST_PLATFORM',
                 '_PYTHON_SYSCONFIGDATA_NAME',
+                "_PYTHON_SYSCONFIGDATA_PATH",
                 'PYTHONPATH'
             }
             old_environ = os.environ
diff --git a/Lib/test/pythoninfo.py b/Lib/test/pythoninfo.py
index 74ebb5e5b8..fa7fbca34e 100644
--- a/Lib/test/pythoninfo.py
+++ b/Lib/test/pythoninfo.py
@@ -326,6 +326,7 @@ def format_groups(groups):
         "_PYTHON_HOST_PLATFORM",
         "_PYTHON_PROJECT_BASE",
         "_PYTHON_SYSCONFIGDATA_NAME",
+        "_PYTHON_SYSCONFIGDATA_PATH",
         "__PYVENV_LAUNCHER__",
 
         # Sanitizer options
diff --git a/Tools/scripts/run_tests.py b/Tools/scripts/run_tests.py
index 445a34ae3e..4077a83424 100644
--- a/Tools/scripts/run_tests.py
+++ b/Tools/scripts/run_tests.py
@@ -42,6 +42,7 @@ def main(regrtest_args):
             '_PYTHON_PROJECT_BASE',
             '_PYTHON_HOST_PLATFORM',
             '_PYTHON_SYSCONFIGDATA_NAME',
+            "_PYTHON_SYSCONFIGDATA_PATH",
             'PYTHONPATH'
         }
         environ = {
diff --git a/configure b/configure
index a1ad0ae251..0657162d1a 100755
--- a/configure
+++ b/configure
@@ -3262,7 +3262,7 @@ fi
     fi
         ac_cv_prog_PYTHON_FOR_REGEN=$with_build_python
     PYTHON_FOR_FREEZE="$with_build_python"
-    PYTHON_FOR_BUILD='_PYTHON_PROJECT_BASE=$(abs_builddir) _PYTHON_HOST_PLATFORM=$(_PYTHON_HOST_PLATFORM) PYTHONPATH=$(shell test -f pybuilddir.txt && echo $(abs_builddir)/`cat pybuilddir.txt`:)$(srcdir)/Lib _PYTHON_SYSCONFIGDATA_NAME=_sysconfigdata_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH) '$with_build_python
+    PYTHON_FOR_BUILD='_PYTHON_PROJECT_BASE=$(abs_builddir) _PYTHON_HOST_PLATFORM=$(_PYTHON_HOST_PLATFORM) PYTHONPATH=$(srcdir)/Lib _PYTHON_SYSCONFIGDATA_NAME=_sysconfigdata_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH) _PYTHON_SYSCONFIGDATA_PATH=$(shell test -f pybuilddir.txt && echo $(abs_builddir)/`cat pybuilddir.txt`) '$with_build_python
     { $as_echo "$as_me:${as_lineno-$LINENO}: result: $with_build_python" >&5
 $as_echo "$with_build_python" >&6; }
 
diff --git a/configure.ac b/configure.ac
index e5fb8bd99e..d444f5ec09 100644
--- a/configure.ac
+++ b/configure.ac
@@ -162,7 +162,7 @@ AC_ARG_WITH(
     dnl Build Python interpreter is used for regeneration and freezing.
     ac_cv_prog_PYTHON_FOR_REGEN=$with_build_python
     PYTHON_FOR_FREEZE="$with_build_python"
-    PYTHON_FOR_BUILD='_PYTHON_PROJECT_BASE=$(abs_builddir) _PYTHON_HOST_PLATFORM=$(_PYTHON_HOST_PLATFORM) PYTHONPATH=$(shell test -f pybuilddir.txt && echo $(abs_builddir)/`cat pybuilddir.txt`:)$(srcdir)/Lib _PYTHON_SYSCONFIGDATA_NAME=_sysconfigdata_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH) '$with_build_python
+    PYTHON_FOR_BUILD='_PYTHON_PROJECT_BASE=$(abs_builddir) _PYTHON_HOST_PLATFORM=$(_PYTHON_HOST_PLATFORM) PYTHONPATH=$(srcdir)/Lib _PYTHON_SYSCONFIGDATA_NAME=_sysconfigdata_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH) _PYTHON_SYSCONFIGDATA_PATH=$(shell test -f pybuilddir.txt && echo $(abs_builddir)/`cat pybuilddir.txt`) '$with_build_python
     AC_MSG_RESULT([$with_build_python])
   ], [
     AS_VAR_IF([cross_compiling], [yes],
-- 
2.34.1

